In the prior art, it is known to remote a switch under control of a remote processor (also referred to as a co-located or angel processor) from a central processor which provides high-level control to the remote switch. The prior art requires that a dedicated link be utilized to interconnect the remote switch with the central processor. One such prior art system is the AT&T 5 ESS as described in the AT&T Technical Journal, Vol. 64, #6, Part 2, July-August 1985. The remote switching module of the 5 ESS is a switching network controlled by a remote processor which is remoted from the center stage switch and the central processor via dedicated T-1 trunk facilities which cannot be switched by an intervening switching network. In addition, co-located with the central processor are other switching modules which are interconnected to the center stage switch and the central processor via special purpose dedicated data links.
The principal problem with this type of switching architecture is one of reliability since the failure of either a link or the central processor disables not only the remote switching network but also any local switching networks co-located with the central processor. In particular, since the central processor controls every switching network in the switching system, failure of the central processor means failure of the entire switching system. To prevent the failure of an individual switching network or the entire switching system, the 5 ESS and other prior art switching systems have duplicated the links and the central processor. Such duplication has proven to be expensive and not entirely satisfactory.
Another problem with the use of dedicated links is that it limits the flexibility in the topology of switching networks with respect to using a plurality of central processors to control a plurality of remote processors and the geographical location of the remote processors. Particularly, such use prohibits dynamically assigning remote processors to different central processors.